This invention relates to an ion source suitably used in an apparatus using ions such as an ion implantation apparatus, an ion microanalyzer, etc.
There has been hitherto known a Freeman type ion source in which a plasma is generated by utilizing a tungsten filament.
In this type of ion source, the tungsten filament is sputtered by the ions, and in a case where a chemically active gas is used as an electric discharge gas, the filament is subjected to a chemical reaction therewith and consequently is worn or damaged easily and remarkably. Therefore, the operation of the ion source has to be stopped for replacement of the filament. Consequently, the apparatus incorporating the ion source also has to be stopped and the operation efficiency of the apparatus is reduced.
In view of the above problems, the applicants of this application have proposed an ion source having an electric discharge chamber partitioned by an anode electrode having a small opening into a main discharge chamber and a subsidiary discharge chamber. A rare gas is introduced into the subsidiary discharge chamber which is provided with the filament. An electric discharge gas for generating the desired ions is introduced into the main discharge chamber. The gas pressure in the subsidiary discharge chamber is kept higher than the gas pressure in the main discharge chamber so that, by effecting a complex electric discharge between the filament, the anode electrode and the main discharge chamber, ions may be generated and, the life of the filament may be prolonged. (Japanese Unexamined Patent Application Kokai (Publication) No. Sho 60 (1985) - 189841).
The foregoing proposed ion source is advantageous in that a chemically active electric discharge gas can be used for a comparatively long time.